Confused about sequential definition
What does this mean exactly? sequential? function Usage: (sequential? coll) Returns true if coll implements Sequential from http://clojure.github.com/clojure/clojure.core-api.html#clojure.core/sequential -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Confused about sequential definition
On Thu, Jul 7, 2011 at 4:48 PM, octopusgrabbus octopusgrab...@gmail.com wrote: What does this mean exactly? sequential? function Usage: (sequential? coll) Returns true if coll implements Sequential from http://clojure.github.com/clojure/clojure.core-api.html#clojure.core/sequential Seems to test for ordered Clojure collections. I get true for seqs, lists, and vectors, but not strings, arrays, java.util.LinkedLists, maps, or sets. So unordered collections and ordered Java collections seem to be excluded. There's also seq? which excludes vectors and coll? which includes maps and sets. All exclude non-Clojure seqables such as LinkedLists, strings, and arrays. None return true for nil. Unfortunately there isn't a built-in predicate function corresponding to will seq work on this?. This inherently works: (defn seqable? [x] (try (seq x) (catch Exception _ false))) producing (seq x) if doesn't throw an exception, false if it does. It's a bit icky but does the job, and has a few useful properties: (if-let [a (seqable? x)] ...) runs the body with a bound to (seq x) if x is seqable and not empty. (if (false? (seqable? x)) ...) catches non-seqables. But it doesn't quite work as a straight predicate if you want nil and empty inputs treated as seqable. You can change that by just adding true on a line by itself after (seq x), but then you have to call seq a second time if you want the seq result, which you usually do. Changing the (seq x) to (if-let [a (seq x)] a ()) will return a truthy value for all objects interpretable as a seq but will turn all empties into a non-nil empty list instead of nil. Another form avoids the icky exception hack and doesn't call seq on its argument: (defn array? [x] (and x (contains? (set (.getName (.getClass x))) \[))) (defn seqable? [x] (or (coll? x) (nil? x) (instance? java.util.Collection x) (instance? java.util.Map x) (instance? java.util.Set x) (string? x) (array? x))) It does do a bit of a hack to test for arrays and it breaks if seq is extended in the future to work with anything it currently won't accept. -- Protege: What is this seething mass of parentheses?! Master: Your father's Lisp REPL. This is the language of a true hacker. Not as clumsy or random as C++; a language for a more civilized age. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Confused about sequential definition
What it means exactly is that there is an interface called Sequential (defined in https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/Sequential.java) that some other interfaces and abstract classes implement or extend, and some clojure data structures that you use implement or extend those, thereby implementing the Sequential interface, and so instances of those data structures will return true for this function. What it means practically, is that the data structure is seqential, like a list or vector, and not like a map. Depending on what you are wanting to use it for, there may be a better function to consider. If you want to explore the relationships in the language, some people seem to like Clojure Atlas: http://www.clojureatlas.com/ http://www.clojureatlas.com/ On Thu, Jul 7, 2011 at 4:48 PM, octopusgrabbus octopusgrab...@gmail.comwrote: What does this mean exactly? sequential? function Usage: (sequential? coll) Returns true if coll implements Sequential from http://clojure.github.com/clojure/clojure.core-api.html#clojure.core/sequential -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Confused about sequential definition
Thank you for the explanations. I saw sequential in an example out on the web. At first, I thought it had something to do with the ordering of a sequence's elements. cmn On Jul 7, 5:22 pm, Mark Rathwell mark.rathw...@gmail.com wrote: What it means exactly is that there is an interface called Sequential (defined inhttps://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/S...) that some other interfaces and abstract classes implement or extend, and some clojure data structures that you use implement or extend those, thereby implementing the Sequential interface, and so instances of those data structures will return true for this function. What it means practically, is that the data structure is seqential, like a list or vector, and not like a map. Depending on what you are wanting to use it for, there may be a better function to consider. If you want to explore the relationships in the language, some people seem to like Clojure Atlas:http://www.clojureatlas.com/ http://www.clojureatlas.com/ On Thu, Jul 7, 2011 at 4:48 PM, octopusgrabbus octopusgrab...@gmail.comwrote: What does this mean exactly? sequential? function Usage: (sequential? coll) Returns true if coll implements Sequential from http://clojure.github.com/clojure/clojure.core-api.html#clojure.core/... -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Confused about sequential definition
On Thu, Jul 7, 2011 at 5:14 PM, Ken Wesson kwess...@gmail.com wrote: (defn array? [x] (and x (contains? (set (.getName (.getClass x))) \[))) (defn seqable? [x] (or (coll? x) (nil? x) (instance? java.util.Collection x) (instance? java.util.Map x) (instance? java.util.Set x) (string? x) (array? x))) It does do a bit of a hack to test for arrays and it breaks if seq is extended in the future to work with anything it currently won't accept. A better extensible way to do this: http://dosync.posterous.com/51626638 David -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Confused about sequential definition
On Thu, Jul 7, 2011 at 6:00 PM, David Nolen dnolen.li...@gmail.com wrote: On Thu, Jul 7, 2011 at 5:14 PM, Ken Wesson kwess...@gmail.com wrote: (defn array? [x] (and x (contains? (set (.getName (.getClass x))) \[))) (defn seqable? [x] (or (coll? x) (nil? x) (instance? java.util.Collection x) (instance? java.util.Map x) (instance? java.util.Set x) (string? x) (array? x))) It does do a bit of a hack to test for arrays and it breaks if seq is extended in the future to work with anything it currently won't accept. A better extensible way to do this: http://dosync.posterous.com/51626638 David Interesting, but there is still going to be a performance issue for the perhaps-common case of testing a non-seqable for seqability: in that case, it will do the reflective check for isArray and it won't use the protocol to cache the result. Making it do so, however, would cause problems if one had (seqable? some-foo) and later attempted to extend the protocol to mark Foos as seqable within the same runtime session. I'm surprised that (.isArray (.getClass foo)) is that slow, though. It may be reflection, but it's not the sort I was given to understand was slow, namely reflective method invocation. An obvious JVM implementation would make the first word of every object a pointer to its concrete Class instance and then the above should be no worse than (.length (.getSomeString some-bean)): a method call and a field lookup in an object whose pointer was the result of another method call and another field lookup in another object. Indeed, both method calls are nonpolymorphic in the former case, since the getClass method is final and the entire Class class is final so isArray is also final. -- Protege: What is this seething mass of parentheses?! Master: Your father's Lisp REPL. This is the language of a true hacker. Not as clumsy or random as C++; a language for a more civilized age. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Confused about sequential definition
On Thu, Jul 7, 2011 at 11:21 PM, Ken Wesson kwess...@gmail.com wrote: Interesting, but there is still going to be a performance issue for the perhaps-common case of testing a non-seqable for seqability: in that case, it will do the reflective check for isArray and it won't use the protocol to cache the result. Making it do so, however, would cause problems if one had (seqable? some-foo) and later attempted to extend the protocol to mark Foos as seqable within the same runtime session. I'm surprised that (.isArray (.getClass foo)) is that slow, though. It may be reflection, but it's not the sort I was given to understand was slow, namely reflective method invocation. An obvious JVM implementation would make the first word of every object a pointer to its concrete Class instance and then the above should be no worse than (.length (.getSomeString some-bean)): a method call and a field lookup in an object whose pointer was the result of another method call and another field lookup in another object. Indeed, both method calls are nonpolymorphic in the former case, since the getClass method is final and the entire Class class is final so isArray is also final. (extend-type Object ISeqable (seqable? [x] (let [c (.getClass x)] (if (.isArray c) (do (extend-type (.getClass x) ISeqable (seqable? [x] true)) true) (do (extend-type (.getClass x) ISeqable (seqable? [x] false)) false) -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Confused about sequential definition
On Fri, Jul 8, 2011 at 12:58 AM, David Nolen dnolen.li...@gmail.com wrote: (extend-type Object ISeqable (seqable? [x] (let [c (.getClass x)] (if (.isArray c) (do (extend-type (.getClass x) ISeqable (seqable? [x] true)) true) (do (extend-type (.getClass x) ISeqable (seqable? [x] false)) false) On Thu, Jul 7, 2011 at 11:21 PM, Ken Wesson kwess...@gmail.com wrote: ... it won't use the protocol to cache the result. Making it do so, however, would cause problems if one had (seqable? some-foo) and later attempted to extend the protocol to mark Foos as seqable within the same runtime session. -- Protege: What is this seething mass of parentheses?! Master: Your father's Lisp REPL. This is the language of a true hacker. Not as clumsy or random as C++; a language for a more civilized age. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Confused about sequential definition
On Fri, Jul 8, 2011 at 1:00 AM, Ken Wesson kwess...@gmail.com wrote: On Thu, Jul 7, 2011 at 11:21 PM, Ken Wesson kwess...@gmail.com wrote: ... it won't use the protocol to cache the result. Making it do so, however, would cause problems if one had (seqable? some-foo) and later attempted to extend the protocol to mark Foos as seqable within the same runtime session. Problem for who? Problem how? Extending seqable? to types you do not control or which are not seqable? as defined by Clojure itself is asking for trouble anyhow. David -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Confused about sequential definition
On Fri, Jul 8, 2011 at 1:06 AM, David Nolen dnolen.li...@gmail.com wrote: On Fri, Jul 8, 2011 at 1:00 AM, Ken Wesson kwess...@gmail.com wrote: On Thu, Jul 7, 2011 at 11:21 PM, Ken Wesson kwess...@gmail.com wrote: ... it won't use the protocol to cache the result. Making it do so, however, would cause problems if one had (seqable? some-foo) and later attempted to extend the protocol to mark Foos as seqable within the same runtime session. Problem for who? Problem how? Extending seqable? to types you do not control or which are not seqable? as defined by Clojure itself is asking for trouble anyhow. If you extend it further at all, it could happen that it gets called on a non-array object of a type before being extended to that type, though this is much more likely at a REPL than in deployment at least. On the other hand if you won't ever extend it further at all there's no real advantage over a non-protocol solution, like the monolithic (or ...)-bodied function punting to a memoized is-array-class? function to check for the array case. -- Protege: What is this seething mass of parentheses?! Master: Your father's Lisp REPL. This is the language of a true hacker. Not as clumsy or random as C++; a language for a more civilized age. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
